This invention relates to a scroll type fluid displacement apparatus, and more particularly to a method for manufacturing the scroll and a tool used in the method.
Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 discloses a device including two scrolls, each having a circular end plate and spiroidal wrap or involute spiral element. Both scrolls are maintained at an angular and radial offset so that both spiral elements interfit at a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbial motion of the scrolls shifts the line contacts along the spiral curved surfaces to change the volume of the fluid pockets. The volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion. Therefore, scroll type fluid displacement apparatus are applicable to compress, expand or pump fluids.
FIG. 1 illustrates a basic design of a scroll suitable for use in a scroll type fluid displacement apparatus. Scroll 1 includes a circular end plate 2 and a wrap or involute spiral element 3 affixed to or extending from one side surface of end plate 2. A scroll type fluid displacement apparatus includes a pair of such scrolls, both of which are maintained at an angular and radial offset so that they interfit and form a plurality of line contacts and axial contact to define at least one pair of sealed off fluid pockets. In such apparatus, each sealed off fluid pocket is defined by the line contacts between interfitting spiral elements and the axial contacts between the axial end surface of each spiral element with the inner end surface of the end plate of the other scroll. The volume of the fluid pocket is thereby defined by both line contacts and axial contacts.
The scroll is generally formed from a single piece of metal by a machining process, such as milling. However, a milling process consumes a great deal of time and energy and, also produces large quantities of waste metal. If the scroll member is formed by casting or forging, and axial dimension of the spiral element is to be made relatively long to obtain a large volume or higher capacity, the draft angle of mold must be made large. After forming in such a mold, the amount of machining of the spiral element to obtain uniform wall thickness increases with the result that relatively large quantities of waste metal are produced. Such a manufacturing method also consumes a great deal of time and energy and, makes it difficult to attain high accuracy of the wall dimensions of the spiral element.